Such a solar receiver is for example suitable for a solar power installation as disclosed in EP 1873397 which discloses a solar power tower to generate electric power from sunlight by focussing concentrated solar radiation on a tower-mounted solar receiver. The solar power tower installation typically includes a “cold” storage tank, a solar receiver, heliostats, a “hot” storage tank, and an energy conversion system, such as a steam generator and turbine/generator set. In operation, a heat transfer fluid is pumped from the cold storage tank to the solar receiver. The solar receiver is typically positioned 50 feet to 250 feet or more above ground and is heated by the heliostats. The heliostats redirect and concentrate solar radiation from the sun onto the solar receiver, which converse solar energy from the incident sunlight to thermal energy. The heat transfer fluid flows through heat exchange tubes of the solar receiver where it is heated by the concentrated solar energy. The heat transfer fluid subsequently transports the thermal energy from the solar receiver to e.g. a steam generator to generate steam, wherein the thermal energy of the steam is used in a steam turbine/generator set to generate electricity. In case of Direct Steam Generation, the heat transfer fluid flowing through the solar receiver is water, wherein steam is directly generated in the solar receiver.
A similar solar receiver is known from a solar power installation which has been built on an industrial scale. The solar power installation has an electrical capacity of at least 5 MWe. The built solar power installation has a field of heliostats which surround a centrally positioned solar power tower. The solar power tower has a top with a height of approximately 80 meters. The solar receiver, comprising a plurality of receiver panels, is mounted in the upper region of the solar power tower. The receiver panels are arranged in groups at different height levels along a circumferential wall of the solar power tower. The groups of receiver panels are mounted above each other. The lowest group of receiver panels defines a superheater. The second group of receiver panels above the superheater defines an evaporator.
The known receiver panel comprises parallel arranged heat exchange tubes which are at both ends connected in a lower and an upper region to an input or output header. The input header distributes a supplied heat transfer fluid, e.g. water in the case of Direct Steam Generation, over the heat exchange tubes. The output header collects the heated fluid to supply it further to a next group of receiver panels, to a separator vessel or to the steam turbine.
The heat exchange tubes of the receiver panel have a straight main portion which is upwards, substantially vertically, arranged in an array. This array of main portions of the heat exchange tubes together form a panel. The straight main portions of the heat exchange tubes are at both sides provided with an inwards extending portion to get a U-shape configuration. The U-shape configuration gives a heat exchange tube a flexibility to expand in a controllable way. The inwards extending portions are single bended and directly connected to one of the headers. The inwards extending portion may give the main portion a freedom to expand and move in a longitudinal, here upwards, direction.
The input and output headers comprise a main conduit with connector organs which are arranged in an array in a length direction. Each heat exchange tube is by its inwards extending portion connected to a corresponding connector organ at the main conduit.
The receiver panels of the known solar receiver have an array of exchange tubes which are held together by a support for arranging the heat exchange tubes close to each other. The heat exchange tubes are kept close together, wherein an individual heat exchange tube is freely arranged to be movable relative to neighbouring heat exchange tubes. The heat exchange tubes are arranged as close as possible to each other to achieve an optimum exchange of heat. Gaps or spacers between the heat exchanges tubes are not desirable as these reduce the rate of conversion of solar to thermal energy by the solar receiver.
A drawback of the known solar receiver is that the headers and other components behind the receiver panel are susceptible for damage caused by high temperatures as a result of heat fluxes from the solar radiation. The headers are located at the top and bottom of the receiver panel. During use the headers may be heated by incident solar radiation. Too much heating may result in damage.
It has been tried to overcome this problem of overheating by arranging shields in front of the receiver panel to cover and protect the headers. The shields may extend along a side edge of the receiver panel to prevent overheating by solar radiation of edge zones of the receiver panel. The prior art shields are made of a ceramic material to withstand the occurring high temperatures caused by concentrated radiation. The application of ceramic shields has not been proved satisfying. First, the ceramic shields reflect a part of the solar radiation that was focussed by the Heliostats on the solar receiver back to the environment and thereby reducing the conversion from solar energy to thermal energy in the solar receiver. Secondly, the ceramic shields have proven to be very vulnerable for damage due to brittleness of the material and the daily warm up and cool down of the shield with sun set and -rise. Summarized, the presence of shields means a loss of solar energy and therefore a strong reduction of a capability to convert solar energy into thermal energy.